Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$151.60	8.819%	$164.9696	$164.97	$164.95	$165.00
Purchase #2	$41.36	12.137%	$46.3799	$46.38	$46.40	$46.40
Purchase #3	$34.94	10.119%	$38.4756	$38.48	$38.50	$38.50
Purchase #4	$88.51	6.515%	$94.2764	$94.28	$94.30	$94.30
Purchase #5	$37.72	8.466%	$40.9134	$40.91	$40.90	$40.90
Purchase #6	$156.81	9.749%	$172.0974	$172.10	$172.10	$172.10
Purchase #7	$78.87	13.690%	$89.6673	$89.67	$89.65	$89.70
7 purchase totals =	$589.81		$646.7796	$646.79	$646.80	$646.90